1. Technical Field of the Invention
The present invention relates to a method of synthesizing shape data by patching partial surface shape data of a free-form surface.
2. Description of the Related Art
When the surface shape of a wide object which cannot be measured by one operation or a complicated solid three-dimensional object which can be measured only from different directions such as a case where shape data of the surface of a mock-up of a vehicle is measured, it is necessary to measure the surface parts of the object from different positions or directions by using a three coordinate measuring machine (digitizer) and to synthesize (patch) partial measurement data obtained.
As methods of synthesizing the partial measurement data, the following methods are conventionally known.
(1) Plural partial measurement data is displayed on a CRT and the operator moves the data while seeing the image so as to coincide overlapped parts with each other (manual method). PA1 (2) Rotation and translation distances of a measuring machine are preliminarily measured and the measurement values are inversely transformed (mechanical measurement method). PA1 (3) Markers such as white or light spots are made by ink or the like and positioning is performed (marker method). PA1 (4) In case of a simple shape such as Z=f(x, y), undetermined multipliers of its analytic surface are fit by an optimization method such as least-squares method (analytic fitting method).
These conventional methods of synthesizing the partial measurement data have, however, the following problems.
According to the manual method (1), the skill of the operator is required and only synthesis with low accuracy can be performed. According to the mechanical measurement method (2), since it is necessary to mechanically rotate or translate the measuring machine, the size of the measuring machine is increased and the machine is complicated. Since an influence of a backlash or the like of the machine is incurred, the method is limited by the mechanical accuracy. According to the marker method (3), since markers are indispensable, the method cannot be applied to an object to which markers cannot be made. An error can also occur by making the markers. The analytic fitting method (4)has the feature that the accuracy which is higher than the mechanical accuracy and is almost equal to the measurement data can be obtained. An object is, however, limited to a simple shape (analytic shape Z=f(x, y)).